semop hanging - Postgres 9.4.4

Hello,

Since couple of days on my Postgres cluster i've seen few times a hanged process. It looks like one of postgres workers stuck on simple INSERT query.

PID USERNAME PRI NICE SIZE RES STATE TIME WCPU CPU COMMAND
12173 postgres 20 0 1372M 345M run 166:18 24.47% 99.90% postgres: db01 db01 10.0.0.101(58713) INSERT

It utilizes 100% of one CPU and after 1-2 hours it starts to utilize memory. After another 1-2 hours OOM-Killer have to take action. At the same time other postgres workers are properly processing queries.

There's no error on syslog/dmesg. Strace:

semop(58261738, {{12, -1, 0}}, 1) = 0
semop(58261738, {{12, -1, 0}}, 1) = 0
semop(58261738, {{12, -1, 0}}, 1) = 0
semop(58851580, {{0, 1, 0}}, 1) = 0
semop(58261738, {{12, -1, 0}}, 1) = 0
semop(58261738, {{12, -1, 0}}, 1) = 0
semop(58261738, {{12, -1, 0}}, 1) = 0
semop(57802972, {{1, 1, 0}}, 1) = 0
select(0, NULL, NULL, NULL, {0, 1000}) = 0 (Timeout)
semop(58261738, {{12, -1, 0}}, 1) = 0
semop(58261738, {{12, -1, 0}}, 1) = 0
semop(58261738, {{12, -1, 0}}, 1) = 0

Is this related to incorrect semaphores configuration?

Here's my current configuration:

sql01:~# ipcs -l

------ Shared Memory Limits --------
max number of segments = 4096
max seg size (kbytes) = 18014398509465599
max total shared memory (kbytes) = 18446744073642442748
min seg size (bytes) = 1

------ Semaphore Limits --------
max number of arrays = 2048
max semaphores per array = 250
max semaphores system wide = 512000
max ops per semop call = 100
semaphore max value = 32767

------ Messages Limits --------
max queues system wide = 32000
max size of message (bytes) = 8192
default max size of queue (bytes) = 16384

sql01:~# ipcs -u

------ Shared Memory Status --------
segments allocated 1
pages allocated 1
pages resident 1
pages swapped 0
Swap performance: 0 attempts 0 successes

------ Semaphore Status --------
used arrays = 257
allocated semaphores = 4369

------ Messages Status --------
allocated queues = 0
used headers = 0
used space = 0 bytes

Some values from postgresql.conf:
max_connections = 4096
effective_cache_size = 12GB
work_mem = 16MB
shared_buffers = 1GB

postgres=# select version();
version
------------------------------------------------------------------------------------------------------
PostgreSQL 9.4.4 on x86_64-unknown-linux-gnu, compiled by gcc (Ubuntu 4.8.2-19ubuntu1) 4.8.2, 64-bit

I would appreciate any help.

Best Regards,

Marcin